Great question. Get It For Me service fulfills requests for books and PDFs from national and worldwide libraries, whereas Summit provides only books from regional academic libraries. You can use either service to request your book. If you request through Get It For Me, the service will try to get your book from a regional library but if none can provide, the service will request the book from  libraries outside the region. Note that if a book is provided through the Get It For Me service, the due date varies from library to library. Often though, a renewal is granted. If you request your book through Summit and a Summit library provides your book, the due date is 6 weeks from check out with no renewals--daily overdue fees apply.

Let me know if you have any other questions.